The Eighth Wonder
by ISpeltEclipseWrong
Summary: Mabel is sick, bored, and lonely. Her friends don't want to catch her flu, and her brother is just itching to go on an adventure although he sticks around to take care of her. Mabel meets a new friend to talk to while she's out of it, but what in the name of God could he really be?
1. Prologue

It should be illegal to be sick in the summer, really. It should be completely and utterly unlawful for whatever bacteria that had made a home of Mabel to be stuffing up her nose, making her head ache, and causing her body to burn with fever. In fact, the annoyed girl was very tempted to do just that, since she was _technically_ a congressman. She let the thought go, begrudgingly admitting it wouldn't do much good. Microbial life wasn't typically inclined to follow the law.

And it was such a nice day outside too! A terrible day to be stuck indoors when there were sights to see, places to go, and people to meet. Or, more importantly; adventures to have, a twin brother to keep out of trouble, and _boys to flirt with_. There were a million things Mabel wished she was doing and she couldn't do any of them. She couldn't do much more than whine in annoyance and discomfort, tossing and turning in hopes of sleeping through the illness. Come on, immune system! Summer wasn't going to last forever, you know, and this was wasting precious potential 'summer romance' time! She was so _bored_.

Her head throbbed and she moaned pitifully, turning to face the wall for the millionth time as if it would be any more comfortable than before. She pulled one of her pillows from under her head, putting it over her ear and pressing down to block out any inkling of sound. The slightest noise made the head ache worse. She let up only when she was having more trouble breathing than usual, and the sound of her own heartbeat pounding in her ears grow annoying. With a groan, she sat up and plucked a tissue from the box on her bedside table. She wiped her runny, raw nose for the hundredth time since she woke up. Really, she thought, the worst part about all this was that she was getting kinda lonely.

The bubbly, extroverted girl who required near-constant socialization and attention was holed up in her room and had been for a few _days_ now. Needless to say, it was killing her. But when her two best friends had shown up cartoonishly bundled in latex gloves and surgical masks, bottles of hand sanitizer on their belts, to cheer her up and help out, Mabel had simply laughed and told them she'd be fine. It was just a little bug, really, she'd could last a few days alone while she got better. She'd be out hanging with them in no time, scoping out the boys and reading trashy novels. _Yes_, she was sure.

They had seemed quite relieved to be let go, the threat of also becoming ill now fading away. Mabel didn't mind, really, but she was sorta blue without her girlfriends to talk to. Although, she wasn't completely alone, she still had-

_Bang_! Mabel flinched as the door smacked into the wall, her clumsy brother tumbling in after it gushing apologies. Speak of the devil, eh? The boy almost lost his footing, very nearly sending the tray in his hands and the bowl of soup on it smashing into a wall, but regained himself at the last second. He grinned sheepishly over at his sister, picking his way over to her bed more carefully.

"Hey, Mabel," he said, setting the tray on her lap which she welcomed with a small smile, "How are you feeling?"

With that, her smile faded away. The sick girl straightened out the tray on her lap, sighing softly. She picked up her spoon, examining it side to side as her mouth opened to reply. There was a pause. She instead opted to let out a low groan, rolling her eyes to the ceiling as if to ask God why they hated her. Mabel let her upper body slump forward, her face comically landing in her bowl of soup. Dipper jumped back in shock as she continued to groan in annoyance, the sound coming out as a quiet gurgle.

Dipper sighed, pulling a handkerchief out of his pocket and handing it to his sister as she sat back up slowly. "That bad, huh?" he asked as she wiped her face clean, nodding glumly, "Well, it's been a few days now, I'm sure it can't last much longer! Besides, you got me looking after you and I'm not going anywhere. As soon as you're over this bug, we'll go on an adventure, okay?"

Mabel smiled up at her brother; her clammy, flushed face and the dark circles under her eyes only portraying a fraction of her usual cheer. "Thanks, Dip," she said picking her spoon back up and eating like a normal person, "you're a good brother." It was nice to have at least one person stick by her without fear of getting sick.

The boy beamed back, scratching his arm as he looked away modestly. "Well..." he drawled, "Yeah. I totally am." He laughed as Mabel halfheartedly hit him in the arm, calling him a jerk. She was still smiling though, so that was good.

They talked for a while more, Mabel catching up on Dipper's progress with the journal and Dipper reluctantly asking about Mabel's 'boyfriends' in an attempt to cheer her up. Nothing interesting in terms of the supernatural had occurred while Mabel was out of it, which Dipper was silently grateful for. He needed his sister to have his back, and visa versa, if they were to face off against otherworldly creatures. Besides, without Mabel, it seemed like it would be less... Fun.

After Mabel was done, Dipper gathered up her dishes along with the majority of the trash that accumulated around her bed for his next trip downstairs. As he passed by her bed, he kissed the top of her head. He told her, as sternly as he could, that she should get some more sleep. She gave him a deadpan expression, telling him that he looked like a kitten when he tried to act serious. He squawked with indignation and she grinned in triumph as she lay back down.

He regained his composure, totally not pouting, and headed back down stairs. After Dipper had flicked off the light, his footsteps receding down the stairs, Mabel could hear him grumbling under his breath about not being cute. She smiled to herself as she fell asleep.

It seemed only a moment until her eyes opened again, the girl not even recognizing that she'd been asleep for several hours at first. As she blinked in the sudden darkness, her confusion faded away after a few dismayed seconds. She figured that she'd must have been asleep, although it hadn't felt like it, and it was around dusk. The last touches of sunlight clung desperately to the sky, and her brother wasn't in his bed yet, so it couldn't have been that late.

She sat up slowly, sniffling in an attempt to clear her nose enough to breathe. Mabel's throat was dry from sleeping with her mouth open, and she briefly debated heading downstairs for a glass of water. A sudden tiredness wiped the idea from her head, the girl not even bothering to fight as she lay back down. Her face was hot and her head hurt, too sleepy to even call out for her brother. He must still be awake, she could hear the television downstairs. It was either that or he'd fallen asleep in Grunkle Stan's chair again.

She turned onto her side, swallowing passed her sore throat as she resolved to get a glass of water in the morning. She felt she'd be better after just a little more sleep. She closed her eyes, lulled by the distant sounds of a 'Why you Ackin' So Cray-Cray?' rerun and her own pounding headache throbbing with her pulse.

But that wasn't her pulse. No, after a few groggy and confused moments of thought, she placed the soft tapping sound out of her head entirely. It was coming from across the room, in the wall above her brother's bed. It was quiet, quiet enough to be mistaken for the girl's own heartbeat and to fade into the background while she slept, but it was there. It was slow enough not to seem deliberate, but it didn't stop after a few minutes. It just kept going.

_Tap_... _Tap_... _Tap_... Almost like a tree branch against a window, but with a bit more 'click'. Maybe it was the pipes in the wall settling? Would there even be pipes there? Mabel didn't know, she didn't build houses for a living, all she knew was that it was weird and she'd never heard it before. She slowly sat up, clearing her dry throat. The tapping seemed to pause, but continued without an inclination that it might have stopped a moment later. Mabel furrowed her brow, pulling the blankets off her legs and standing shakily.

She should go get her brother, she knew. She wasn't a damsel in distress from a horror movie, or someone who died in the first five minutes of a ghost show; she knew there were otherworldly things in this town, and she knew they were dangerous. Still, this was her home. This was the room her brother and her shared. She felt safe here, and if she needed Dipper she could always call out. She shuffled over to the other side of the room, following the tapping sound, and sat at the edge of her brother's bed.

Now that she was here, it became apparent that the sound was coming from deep within the wall. She crawled over Dipper's bed to get close to the sound, face scrunched up from the throbbing in her head and concentration. After a moment, she carefully pressed her ear to the wall. Yes, it did sound like from it was further back and it did sound like the clink of a pipe or something hard against wood. She didn't know why a pipe would be up here if all the plumbing was on the ground floor, but it seemed the mostly likely answer to her muddled brain. Nothing to be worried about. Maybe it wasn't even a pipe, but a heating vent. Yes, that would make more sense.

She started to move away from the wall, wriggling to get back to the floor and back to her own bed. She was tired, and she really shouldn't be getting up when she didn't have to. She paused once again as a shiver ran down her spine, causing the girl to twitch with a sudden rush of heebie-jeebies. Oh, that felt weird and_ not good_. She looked back to the wall. She felt that something was watching her. She swallowed again, her spit doing nothing against her dry mouth, and shifted back towards the wall.

She'd gone from simply curious to serious, but if it turned out to be nothing and she ran to her brother... Well, she'd just feel silly and not the _good_ kind of silly. There was nothing wrong with investigating though, nothing bad-silly about that, just to make sure there was something to actually be worried about.

She pressed her ear back to the wall, hearing the heating vent within tapping steadily as if chills hadn't just ran down Mabel's spine. It didn't react to her feelings, it was an inanimate object for god's sake. Maybe they had rats, she thought, the Mystery Shack wasn't exactly up to code after all. She let herself be grossed out about the thought of a rat watching her for a second before returning to the task at hand.

She listened for a few minutes more, the steady tapping almost putting her to sleep before she seemed to move on her own. She lifted her hand, fingers wrapped into a loose fist. It was _tapping_, not _knocking_. The work of some part of the house or some pest, but not a conscious action! She had to be sure, though, and hell, maybe hearing actual knocking would let her see how bad-silly she was being.

She rapped on the wall firmly, like she was knocking on a door. _Knock, knock._

There was no answer, no _anything _actually. Silence. The tapping had stopped. Mabel breathed a sigh of relief, maybe the heater had turned off for the time being and she could get some sleep. She was moving away from the wall when she stopped.

_**Knock, knock.**_

_~Gravity Falls Theme Plays~_

A/N: Spooky, huh? And no, I'm afraid it isn't Wax Larry King in the vents this time, but something more sinister. Would anyone care to guess what this fanfiction's Monster of the Week is? No? Don't worry, it will all be revealed in time. Mwahahahaha...

I have big plans for this story. BIG PLANS. If you liked this chapter, please feel free to review/follow/favorite, I'd love to know what you think!

Gravity Falls belongs to Disney, I don't claim any ownership of Alex Hirsch's work!


	2. Chapter 1

"Whoa!"

Mabel was startled, to say the least. She whipped her head around so quickly it was a miracle she didn't get whiplash, although a section of her hair did come around and hit her in the face. She wasn't scared, not yet, her mind still processing the surprise of the answering knock. The sound had gone from tapping deep within the wall to knocking, deliberate and clear, right over the spot she'd rapped on. A few long seconds stretched as her overheated mind fell over itself, trying to make sense of what just happened.

She brushed away strands of hair from the side of her mouth, eyes narrowing. She leaned in closer to the wall as she debated the possibilities of _giant_ rats, delayed echoes, or the gnomes trying to kidnap her again. She moved back at the last thought. Yeah, not happening, she didn't like being kidnapped. She had to go get her brother and Grunkle Stan right _now_. She was slipping off the side of the bed when a thought occurred to her. It had been about a minute since the last knock, so what if she just imagined it? What if there was nothing in the wall-

_**KNOCK, KNOCK, KNOCK, KNOCK!**_

The sudden loud noise sent Mabel jumping in fright, tumbling backwards off the edge of the bed so hard she whacked her head against the floor. The momentum kept her going until she'd flipped over and onto her knees, hands raising to her head as she groaned in pain. Her sickness induced headache just got about a million times worse, and she was too disorientated to get up right away.

The knocking hadn't stopped with her shock and still something within the wall was banging against the wood. It must have been knocking on a stud, because from the apparent force of it they would have broken through the drywall by now. Mabel shook her head to banish the ringing, rubbing her eyes to rid them of the stars she was seeing. She got her feet under her and stood up as quickly as she could without falling over.

The knocking stopped. She stumbled over towards the attic door, feeling her skull gingerly with her fingertips. No bump yet, so that was good. Maybe if she got ice on it quickly, there would be no swelling at all... The dizziness was passing now and she sped up in response; she didn't know how long that wall would hold whatever the hell that was. The girl whined as a final wave of dizziness seemed to make the floor and ceiling change places, but managed stayed on her feet through sheer stubbornness. She was fiddling with the door handle when she heard a raspy breathing behind her.

_Wheeze, __gasp! __Wheeze, __gasp!__ wheeze.._.

She froze in her tracks, a stupid instinct to freeze up in the face of danger, slowly turning her head to look at the wall again. It was intact, _thank god_, since she'd half expected whatever it was to have broken out by now, but there was definitely something alive in there. The raspy breathes, which Mabel found herself unable to tell if they belonged to a person or an animal, slowly transformed into the growls and chatters of an angry ferret. If that ferret was the size of a smart car and was currently being drowned.

"D-" she mumbled, her voice so quiet as she struggled to use it through her surprise and dizziness. It sounded less like the start of her brother's name, and more like she was about to vomit, "Dip-"

The chatters turned even more gargled like talking through a throat filled with phlegm. Mabel could relate at the moment with this dumb cold. Then it morphed, and in seconds it was the pitch-perfect replica sound of a _baby gurgling_.

Nope. Nope, nope, nope. All aboard the Nope-Train to Screwthatville.

"Dip-!" she tried again, heart squeezing in her chest as her eyes widened with terror. Mabel felt like she was in one of those nightmares where you can't run or call out, or like she was drowning in slow motion.

What the hell _was _that thing? She'd never read anything about something that gurgled like an infant, not even in Dipper's book. It seemed silly compared to other things she'd seen, but the notion of a monster mimicking something so human and so innocent _so perfectly_ was disturbing. She hoped it didn't start crying in that voice, she didn't think she could handle that.

She tried again, finally regaining her voice as she screamed.

"_DIPPER_!"

She jiggled the handle of the door, tumbling through as it finally gave in. She ran down the stairs, taking them two at a time and nearly breaking her neck when she slipped. She thankfully just went down the half-flight on her butt instead and rolled back onto her feet at the bottom. She slid on socked feet as she tried to turn her body too quickly, wrenching herself in the direction of the living room. Her feet pounded against hardwood as she followed the sounds of 'Baby Fights' from the television.

She gripped the side of the door frame, skidding to a stop. Her hair was wild, tangled with bedhead and flying about her face, and there was a frightened look in her eyes. "Dipper!" she cried, but the name died on her lips. The room was empty, the television entertaining only itself. Before Mabel could worry herself sick about where her brother was, whether he was alive or not, she spotted a note on top of the TV.

She hopped down into the living room, jogging over to the television. She pushed the button absently, plunging the room into sudden quiet and near-darkness. She plucked the note from the dust-covered appliance, recognizing Dipper's writing immediately.

_'He__eee__y, Mabel..._

_Sorry I'm not here. I'm so, so, so sorry. I know I said I'd stay, but guess what! I was outside doing some chores, and I saw an honest-to-God elf run by into the woods! Yes, I'm sure it was an elf and not a gnome. I just had to go after it, you know? And you're asleep right now, so I'll probably be back before you get up anyway. This is great! I haven't even read much about them in the book. Maybe the author wrote about elves in one of the other potential journals? Anyway, I gotta go! I have to hurry if I'm going to catch it, it seemed pretty fast. I'm going to ask it if Santa's real or how to get into Mordor or something._

_Dipper'_

'He ditched me,' Mabel thought, 'He ditched me to go on an adventure all by himself and now I'm going to _die_. I'm going to die _SINGLE_.'

She had to hold that train of thought when the sound of distant scuttling reached her ears, it was coming from the top of the stairs and was getting closer quickly. She dropped the scrap of paper and took off, heading passed the kitchen and turning down the hallway towards Stan's room.

"Grunkle Stan! _Grunkle Stan!_" she called, skidding to a stop. She slapped a hand against her forehead, groaning at her own absentmindedness. Grunkle Stan wasn't here, he'd said something about a lodge and had gone off to do old man things this afternoon. Who else could help?...Wendy and Soos had both gone home for the day. Mabel was home alone with the baby-sound-making thing in the walls. She turned around and ran back to the kitchen.

She looked around desperately, hearing the scuttling get closer. Her eyes fell on the cutlery drawer and she tugged it open, grasping a steak knife from its depths and gripping it tight. She'd need some way to defend herself when and if the unknown creature escaped the wall. She clutched it in both hands, holding it in front of her pointing forwards. If it jumped at her, this knife was going directly into its stomach. She just needed to get to the front door and out of the shack.

She walked slowly and carefully, she didn't want to stab herself, keeping her ears focused for any sound in the walls. She could hear it moving around, but always just a bit too far away or a bit too fast for her to place it. It hadn't made another vocalization since the bedroom. She was almost to the door now. She let out a sigh of relief when she saw it, foolishly dropping the knife as she rushed forwards.

She was sniffling and coughing as she unlatched the door, tugging it open with some difficulty. Ugh, she was really too sick for this. She was so distracted by the sounds of her own illness, she didn't hear the scuttling quickly approaching behind. There was a loud thump from under the stairs, right beside the door. She froze.

"Well, you're certainly jumpy this evening, Miss Irving," it said. Its voice was high-pitched and had a chattering quality to it, like an animal was trying to talk. Now that it spoke with words, it didn't sound any larger than a small dog or a very large rat. "You really should stop this running around, you're ill. You've nearly killed yourself three times in the past five minutes."

Mabel stopped, resisting the urge to run out the now open door. She really should, she wasn't sure of this creature's intentions yet after all, but she wouldn't get answers if she ran screaming for the hills now would she? Besides, what if Dipper came back after she'd ran off? She stepped back, pulling the door closed again. She turned around, but found the source of the voice wasn't to be found. He was still hiding, apparently.

"Um, hi?" No use making the potentially dangerous creature angry. It seemed to know how to speak politely at least, "Who... What are you?" she asked, leaning against the door. She shouldn't have dropped that knife.

"A very, very clever mongoose."

_~Commercial Break~_

A/N: Darn it, Dipper. You're suppose to be looking after your sister, not chasing after elves! Now you've left here with... whatever... and she may or may not die! Gosh, your brother instincts are way off the mark today. Some huge hints about the monster of the week here, if you know who he is then you'd be able to guess it by now.

I don't even know _why _I'm making you guess. I suppose it just sound more fun then straight up telling you.

Sorry for not making Mabel very wacky or this chapter very funny, but hey! She's running for her life and she's sick. The chuckles will come later in true Gravity Falls fashion, I swear. I hope there isn't many spelling/grammar errors, but my beta told me it was okay so I'll take her word for it. Please comment what you think! :

Gravity Falls belongs to Disney, I don't claim any ownership of Alex Hirsch's work!


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